Hi guys,

What kind of usable rpm gain will I get on my stock 305 tpi motor after I put my hooker 2055s and new magnaflo cat on?

Right now the power goes flat at 4500 or so, I'm hoping she'll pull to 5000.

I kinda need to know because I need to select rear gears for my other axle. I think 3.42 or so would be fine, but I'd go deeper if the motor could actually use the extra teeth.

Thanks,

 

Thats where TPI dies. Its a well known fact. You need to get the TPI flowing more in order to gain more from headers. You will probably get more HP and a better pull by puttin the headers in.
Now, you should check the article on porting your TPI intake, and it should help you reach your goal. I think

 

not real encouraging, though I'll take what I can get. Sounds like 3.42s will be my best go. thanks

 

Its really easy to think about.

In order for an engine to push more air out it will need to take more air in. TPI's die at 4500RPM. Thats how they are from the factory. So, you took care of one problem. You solved the "push the air out" part, now you have to solve "pull the air in"!

You shouldn't get discouraged. As a matter of fact, you're half way there. Porting the plenum should be easy.

 

Oh I'm not really that discouraged. I've just never owned an engine before that need headers and porting to pull to 5k. Years ago, I had a 383 dodge with a two barrel carb that ran out of nuts about where this 305 does. The 305 is better on gas, though. lol

 

Uh, porting ain't the end of the story.

The "T" in "TPI" stands for "tuned". As in, the port runner length is "tuned" to provide the best pulse density effect for a certain RPM range. With stock TPI, that RPM range tops out at around 4500 RPMs.

You want higher RPMs, you need shorter runners (aftermarket). They'll also have a larger cross-section for higher flow capability. The Edelbrock version runs around $350.

 

Now you really discouraged him .

I understand what you are saying, but porting should help. I don't see why he shouldn't do it. Its free!

 

Didn't say he shouldn't. But, don't expect gains in the RPM range. It may help power up to peak, but won't have a significant effect on how high the engine will spin. And, the stock runners will still be a choke point (as will the stock base).

Don't forget, the cam plays a major role in this game. The factory designed these parts to work together to get the best seat-of-the-pants demo ride feel. That does not translate to impressive ET or peak power numbers.

Assuming you already have the equipment for it.

 

Put on your headers, siamese the base a few inches in and call it a day. Oh and for another slap in the face, the cam needs to be swapped out, it has a small duration. BTW revving past 4500 sure as hell doesn't mean you're making power past it, my 350 TPI will flat line at about 5300 but will still pull past that straight on to the 6700rpm limiter if i let it.